Sensors serve to detect process variables in automation technology that, for example, are integrated in fill-level measuring devices, flow measuring devices, pressure and temperature measuring devices, analytical measuring devices, etc. The devices detect the corresponding process variables: the fill-level, flow, pressure, temperature, analytical data such as the pH, opacity, or conductivity. Actuators, such as, for example, valves or pumps, are used to influence process variables. The flow rate of a fluid in a pipeline section or a fill-level in a container can thus be altered by means of actuators. Sensors and actuators are generally designated field devices. In conjunction with the invention, field devices accordingly designate all devices which are process-oriented and which provide or edit process-relevant information.
German patent, DE 10 2012 109 632 A1 discloses a measuring sensor for the meteorological detection of a pressure to be measured as relative pressure in comparison to a reference pressure that predominates in the surroundings of the measuring sensor. The measuring sensor has the following components: a housing, a relative pressure sensor arranged in the housing, a pressure supply by means of which the pressure to be measured is supplied to the relative pressure sensor, and a reference pressure supply by means of which the reference pressure is supplied to the relative pressure sensor. The reference pressure supply terminates in an opening in an outer wall of the housing, against the outside of which the reference pressure acts. A closure is inserted in an end region facing the opening that seals to the outside the inner chamber of the reference pressure supply located on the side of the closure facing away from the opening. Moreover, a capillary tube is provided through which a region of the reference pressure supplier located on the side of closure facing away from the relative pressure sensor is connected by a hole leading through the closure to the inner chamber of the reference pressure supply sealed by the closure.
This solution prevents moisture from entering the interior of the reference pressure sensor. It should be noted that the penetration of moisture substantially impairs the measuring precision of the measuring sensor and, in an extreme case, can lead to the complete failure of the pressure-measuring pressure sensor.
German patent, DE 20 2011 108 899 U1 discloses a relative pressure-measuring transducer that has a housing, a pressure sensor with a pressure-measuring transducer for providing a pressure-dependent electric primary signal, and an electronic circuit for driving the pressure-measuring transducer and for processing the primary signal in order to provide a primary-signal-dependent signal as a measured value at an output of the electronic circuit. The pressure sensor and the electronic circuit are arranged in the housing. The housing has a media pressure opening and a reference air path, wherein a pressure sensor can be supplied with media pressure through the media pressure opening, and with surrounding air through the reference air path for providing the atmospheric pressure. The reference air path comprises a filter element that protects the pressure sensor against the penetration of moisture. The reference air path has at least two reference air openings in a surface of the housing, wherein at least one opening path runs from each filter element to the reference air opening. The opening paths are positioned and oriented relative to each other such that an opening path runs from at least one filter element to a reference air opening without an ascent. This allows water to drain from the filter element.
German patent, DE 10 2008 018 900 A1 discloses a pressure-equalization threaded joint with a tubular membrane and adjustable volumetric flow. The pressure-equalization threaded joint has a breathable, semipermeable leadthrough, and consists of a bottom part and a cover as the top part. The two parts are connected to each other. The bottom part is formed by a hollow cylinder. Radial ventilation channels are provided between the top edge of the bottom part and the cover. The tubular membrane is arranged in the hollow cylinder of the bottom part. The axial dimension of the tubular membrane is selected such that its top edge is in contact with the inner surface of the cover, and its bottom edge is in contact with an inner surface bordering the hollow cylinder of the bottom part.
Since the flexible tubular membrane does not have a specific contact surface in the radial direction and is not attached in a form fit in the pressure-equalization threaded joint, the danger exists that an inflowing or outflowing gaseous medium will not follow the path identified in FIG. 5, but will rather flow along the top or bottom edge of the tubular membrane and leave the housing unfiltered through the radial opening 49, or will flow unfiltered into the housing.